Propellant powder and process for making same



PRUPELLANT POWDER AND PROCESS FOR MAKING SAME .loseph Cohen and Eli D. Bessel, China Lake, Calif.

No Drawing. Application January 23, 1952, Serial No. 267,906 I 3 Claims. (Cl; 102-98) (Granted under Title 35, U. S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore.

This invention relates to propellant powders and more particularly to internal burning powder grains which are treated to provide a combustion inhibiting film on the outside surface.

The development of the internal burning grain for rocket motors has been in progress since World War II. With this type of grain the motor tube is not exposed to rapidly moving hot gases, and as a consequence the trend in design has been toward the use of lightweight metal motor tubes. This has resulted in more emphasis on the reliability of restricting materials which inhibit burning on specified areas of the grain during the entire course of combustion.

Inhibiting methods employed in the prior art involve wrapping or coating the powder with materials which are less flammable or slower burning than the powder itself. In such methods, separation of the inhibitor from the powder, cracking of the inhibitor, and cracking of the powder grain often occur. The nitroglycerin of double base powders migrates into the inhibitor coat ing as does the plasticizer used in the powder. In the reverse direction, the inhibitor plasticizers employed migrate from the inhibitor into the powder. These migrations cause such final efiects as explosion on firing, uncontrolled and erratic burning of the powder during firing, misfires, and erratic trajectories. Such coatings are often expensive, have an appreciable bulk, and are applied by an involved manufacturing process. In the instant invention, an inhibitor coating derived from the powder grain by a chemical treatment is employed to control burning characteristics of the powder.

The invention also comprises a method of chemically treating powder in the manner indicated to form a relatively slow burning inhibitor coating on the outer surface of the powder grains.

An object of this invention is to provide a surfacecoated propellant powder.

Another object is to provide a process for producing said improved surface-coated powder.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following description.

The preferred process of-treatment is as follows: The powder grains are dipped in a water and ethanol solution containing 10% by weight of ammonium sulfide. The water to alcohol ratio is 2:1. the solution ispreferably kept below 40 C. The film nited States Patent iatented Jan. 29, 1957 cellulose which is produced from the nitrocellulose The temperature of thickness is controlled by the time, required for penetration of the reactants into the powder. time of two hours gives an inhibitor thickness of about 0.02 inch if the temperature of the solution is kept between 28 and 32 C. The powder grain is next rinsed in water at about 30 C. and then immediately dipped into a bath of glycerin. The powder grain is A treatment originally present'in the powder grain. This film' is an integral part of the grain and is very securely bound thereto. Since neither solid nor adhesive is used to attach the inhibiting film to the powder grain, there is no. problem of inhibitor coating separation due to adhesion flaws. The film of regenerated cellulose is plasticized with glycerin and is quite pliable. An important advantage of the cellulose film is that it is a barrier to nitroglycerin and to plasticizers commonly incorporated in propellant powders. Furthermore, .unreacted nitrocellulose in the powder grain does not absorb glycerin so the problem of inhibitor cracking, due to migration of its plasticizer, does not exist.

It will be evident that inhibitor coatings may be produced from the nitrocellulose present in either single base or double base powders, and that coatings may be plasticized by compounds other than glycerin. The imperviousness of cellulose films to nitroglycerin is useful in the preparation of thick powder coatings which are impractical to produce by chemical action alone. A relatively thick layer of plastic or other inhibiting material may be added directly to the treated powder grain by, for example, wrapping, extruding, or dipping. The nature of cellulose prevents migration of either explosive or plasticizer, and the fiexiblity of the plasticized coating prevents the cracking of the powder grain or the outer layer- Although the foregoing description has particular reference to the use of ammonia, ethyl alcohol, and hydrogen sulfide to modify the surfaces of the powder grain, it should be clearly understood that this is merely the preferred form, and that the denitration procedure is not limited to the action of the above-named reagents. For example, hydrazine in water-methanol solution is a useful reducing agent in the process.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specificallydescribed.

What is claimed is: V

1. The process of producing a coated nitrocellulose containing powder grain of improved burning eharacteristics which comprises treating a nitrocellulose powder grain immersed in a solution including ammonia and ethyl alcohol with hydrogen sulfide.

2. The invention defined in claim 1 comprising in addition the step of immersing the treated powder grain in glycerin for a time sutficient to allow maximum ab- 'sorption by said glycerin'by said film.

3. The process comprising immersing a nitrocellulose containing powder grain in a 2 :1 water-ethanol solution containing 10% by weight of ammonium sulfide for a time sufiicient to form a denitrated film on said grain, rinsing said grain, and immersing said grain in glycerin for one to two hours.

References Cited in the file of this patent UNITED STATES PATENTS 

3. THE PROCESS COMPRISING IMMERSING A NITROCELLULOSE CONTAINING POWDER GRAIN IN A 2:1 WATER-ETHANOL SOLUTION CONTAINING 10% BY WEIGHT OF AMMONIUM SULFIDE FOR A TIME SUFFICIENT TO FORM A DENITRATED FILM ON SAID GRAIN, RINSING SAID GRAIN, AND IMMERSING SAID GRAIN IN GLYCERIN FOR ONE TO TWO HOURS. 